Magnetostriction is a small deformation caused by the magnetization of magnetic substances. The deformation between dimensions at the demagnetized state of a magnetic substance and at saturation magnetization state is conversed into an amount per unit length, which is called “saturation magnetostrictive coefficient”, or simply “magnetostrictive coefficient”. The magnetostrictive coefficient shows different values for the easy axis magnetization and the hard axis magnetization, and also shows elongation and contraction in accordance to the magnetization. Magnetostrictive coefficient also changes its value as a function of temperature. In the fields of physics and engineering, the magnetostrictive coefficient having these characteristics is one of the basic properties unique to the substance.
Recently, magnetostriction in the field of industry, is utilized as a magnetostrictive actuator (see Japanese Patent No. 3332125 Magnetostrictive actuator for reference) or a magnetostrictive sensor utilizing the reverse effect of magnetostriction (see Japanese Patent No. 3521010 “Magnetostrictive sensor” for reference), or a magnetostrictive torque sensor (see Japanese Patent No. 3526750 “Magnetostrictive torque sensor” for reference), or a magnetostrictive stress measurement (see Japanese Patent No. 2771433 “A measurement method of magnetostrictive stress of tubes” for reference).
The magnetostrictive coefficient as a basic property unique to the substance, is generally measured by strain gauge method or capacitance method (for example, see Etienne du Trémolet de Lacheisserie Magnetostriction: theory and applications of magnetoelasticity, CRC Press, Boca Raton, 1993 for reference). This is classified as an external magnetostriction, which is an amount obtained by macroscopic observation of the deformation of a magnetic substance between dimensions at demagnetized state and at saturation magnetization state. For the measurement of the magnetostrictive coefficient in the external mode with this method, it must be noted that the confirmation that the magnetization is sufficiently approaching to the saturation is necessary.
As opposed to this, the crystallographical magnetostrictive coefficient is known. This value is not detected except by using an X-ray diffraction method or a neutron diffraction method by measuring a change in the lattice spacing. Especially, in a magnetic substance consisting of two or more kinds of elements, the magnetostriction defined as the relative change in the location of the atoms in a unit cell is called an internal magnetostriction (see above mentioned Magnetostriction: theory and applications of magnetoelasticity for reference).
Now, the macroscopic external magnetostrictive coefficient and crystallographical magnetostrictive coefficient may be different values, according to the definition. However, if the sample is a single crystal consisting of one kind of element, our interest is their values at saturation magnetization the values would show the same.
As for the method of measurement of this crystallographical magnetostrictive coefficient, the above mentioned X-ray diffraction method and neutron diffraction method are useful, but conventionally, both were poor in resolution, and could only be applied to substances that showed large magnetostrictive coefficients. Therefore, X-ray diffraction method was not applied as a practical method (see above mentioned Magnetostriction: theory and applications of magnetoelasticity for reference), and was seldom used.
FIG. 1 is a schematic diagram to explain exemplifies the relation between the angle of incidence θ and the intensity of X-ray diffraction I of a rocking curve, in which the vertical axis refers to the intensity of X-ray diffraction I and the horizontal axis refers to the angle of incidence θ. In FIG. 1, the rocking curve profile I(0, θ) at the demagnetized state is shown in a solid line, and the rocking curve profile I(H, θ) at the saturation magnetization state at magnetic field H is shown in a broken line, for a sample. In the conventional crystallographic method for measuring magnetostriction using X-ray diffraction, scanning the incident angle by a high resolution goniometer, and the Bragg angle (the angle that gives the peak point for the rocking curve profile in FIG. 1) at the demagnetized state θB(0) and the Bragg angle at the saturation magnetization state θB(H) were measured, and as shown in FIG. 1 as A, a Bragg angle shift ΔθB was calculated from the difference between the θB(0) and θB(H), which was converted into the change of the lattice spacing in order to calculate the magnetostrictive coefficient. However, the rocking curve being flat near the peak point, determining the angle of the peak point often gave uncertainty, and thus the direct measurement of the difference between these angles was not useful.
As opposed to this, in recent years, the present inventor et al. have improved the sensitivity with the X-ray diffraction method by two orders, as compared to the conventional method, and have provided a practical accuracy for the measurement on one of the typical magnetic materials. (See Arakawa, Etsuo; Nishigaitsu, Hidetaka; Mori, Koichi; Maruyama, Koh-ichi, Magnetic Science Joint Symposium 2004, 2004, 3AP22 for reference)
Specifically, the present inventor et al. have presented a method for determining the magnetostrictive coefficient with high sensitivity (Non-patent literature 3), in which the diffractometer was fixed near the intensity inflexion point (IP) of the rocking curve (see FIG. 1 for reference), while the diffraction intensity change ΔI caused by the existence or nonexistence of magnetization was measured with sufficient photon statistics, which was compared to the amount calculated by differentiation of the rocking curve, and as indicated in FIG. 1 as B, the Bragg angle shift ΔθB was calculated by the division of ΔI and I(0,θ) as will hereinafter be described, which was converted into the change of lattice spacing. The outlines of this method will be described below.
FIG. 2(a) shows a schematic diagram to explain the relative intensity change of X-ray diffraction in accordance to the strength of magnetic field H, in which the vertical axis refers to the relative intensity change δ axis, and the horizontal axis refers to the magnetic field H axis. FIG. 2(b) shows a schematic diagram to explain the relation between the strength of magnetic field H and the asymmetry component δA to the magnetic field of the above mentioned relative intensity change δ, in which the vertical axis refers to the asymmetry component δA, and the horizontal axis refers to the magnetic field H axis. FIG. 2(c) shows a schematic diagram to explain the relation between the strength of magnetic field H and the symmetry component δS to the magnetic field of the above-mentioned relative intensity change δ, in which the vertical axis refers to the symmetry component δS, and the horizontal axis refers to the magnetic field H axis. In FIG. 2(a), the solid line represents the property measured during ascending magnetic field, and the broken line represents the property measured during the descending magnetic field, and in FIGS. 2(b), 2(c), the solid line represents the property during ascending magnetic field (equivalent to the hereinafter described equation [No. 3] and equation [No. 4] respectively), and the broken line represents the corresponding property calculated during descending magnetic field (equivalent to the opposite signs of δA and H in hereinafter described equation [No. 3] and H in hereinafter described equation [No. 4], respectively). The relative intensity change δ of X-ray diffraction shown in FIG. 2(a) is expressed as follows
                    [                  No          .                                          ⁢          1                ]                                                                                  δ            ⁡                          (                              H                ,                θ                            )                                =                                                    Δ                ⁢                                                                  ⁢                                  I                  ⁡                                      (                                          H                      ,                      θ                                        )                                                                                                I                  _                                ⁡                                  (                                      0                    ,                    θ                                    )                                                      =                                                            I                  ⁡                                      (                                          H                      ,                      θ                                        )                                                  -                                                      I                    _                                    ⁡                                      (                                          0                      ,                      θ                                        )                                                                                                I                  _                                ⁡                                  (                                      0                    ,                    θ                                    )                                                                    ⁢                                  ⁢        where                            (        1        )                                [                  No          .                                          ⁢          2                ]                                                                                  I            _                    ⁡                      (                          H              ,              θ                        )                          =                                                                    ⁢                                          I                ⁡                                  (                                      H                    ,                    θ                                    )                                            ⁢                                                                                                              0                      <                                                                        ⅆ                          H                                                /                                                  ⅆ                          t                                                                                                      ⁢                                      +                                          I                      ⁡                                              (                                                                              -                            H                                                    ,                          θ                                                )                                                                                                                                                                          ⅆ                      H                                        /                                          ⅆ                      t                                                        <                  0                                                              2                                    (        2        )            I(H, θ) is the diffraction intensity at magnetic field strength H, observed at an angle of incidence θ close to the Bragg angle. If the relative intensity change of the X-ray diffractions was measured at ascending magnetic field 0<dH/dt and at descending magnetic field dH/dt<0, the component δA asymmetry to the magnetic field shown in FIG. 2(b), and the component δS symmetry to the magnetic field shown in FIG. 2(c) are given,
                    [                  No          .                                          ⁢          3                ]                                                                                  δ            A                    ⁡                      (                          H              ,              θ                        )                          =                                            δ              ⁡                              (                                  H                  ,                  θ                                )                                      ⁢                                                                                                  0                    <                                                                  ⅆ                        H                                            /                                              ⅆ                        t                                                                                            ⁢                                  -                                      δ                    ⁡                                          (                                                                        -                          H                                                ,                        θ                                            )                                                                                                                                                        ⅆ                    H                                    /                                      ⅆ                    t                                                  <                0                                              2                                    (        3        )                                [                  No          .                                          ⁢          4                ]                                                                                  δ            S                    ⁡                      (                          H              ,              θ                        )                          =                                                                    ⁢                                          δ                ⁡                                  (                                      H                    ,                    θ                                    )                                            ⁢                                                                                                              0                      <                                                                        ⅆ                          H                                                /                                                  ⅆ                          t                                                                                                      ⁢                                      +                                          δ                      ⁡                                              (                                                                              -                            H                                                    ,                          θ                                                )                                                                                                                                                                          ⅆ                      H                                        /                                          ⅆ                      t                                                        <                  0                                                              2                                    (        4        )            respectively. The symmetry component δS to the magnetic field is the subtraction (δS=δ−δA) when δA is subtracted from δ. For evaluating the magnetostrictive coefficient, in the relative diffraction intensity change δ, only the symmetry component δs, to the magnetic field, was used, and the asymmetry component δA, to the magnetic field, was not used.
By combining the rocking curve profile at the demagnetized state I(0, θ) shown in a solid line in FIG. 1 with its differential coefficient dI(0, θ)/dθ, another relative diffraction intensity change D(θ) is defined.
                    [                  No          .                                          ⁢          5                ]                                                                      D          ⁡                      (            θ            )                          =                              -                                                                                            ⁢                                  ⅆ                                      I                    ⁡                                          (                                              0                        ,                        θ                                            )                                                                                                  ⅆ                θ                                              ·                                    Δθ              B                                      I              ⁡                              (                                  0                  ,                  θ                                )                                                                        (        5        )            By comparing this relative intensity change D(θ) to the symmetry component δS obtained in equation [No. 4], the difference from the Bragg angle θB at the demagnetized state, in other words, the shift ΔθB of the rocking curve (indicated in FIG. 1 as B) can be determined.
The fact that the magnetostrictive coefficient λ100, when the magnetization is oriented along one of the magnetization easy axis, neglecting the volume change, can be obtained using the shift ΔθB of the rocking curve by the following equation
                    [                  No          .                                          ⁢          6                ]                                                                                  λ            100                    ⁡                      (            H            )                          =                              2            ⁢                          (                              cot                ⁢                                                                  ⁢                                  θ                  B                                            )                        ⁢                          Δθ              B                                =                                                                                ⁢                                                δ                  S                                ⁡                                  (                                      H                    ,                    θ                                    )                                                                                    -                                  1                  2                                            ·                                                ⅆ                                      I                    ⁡                                          (                                              0                        ,                        θ                                            )                                                                                        ⅆ                  θ                                            ·                                                tan                  ⁢                                                                          ⁢                                      θ                    B                                                                    I                  ⁡                                      (                                          0                      ,                      θ                                        )                                                                                                          (        6        )            as a value with a practical accuracy at the saturation magnetization state, is a method which the present inventor et al. have made publicly known (See Arakawa, Etsuo; Nishigaitsu, Hidetaka; Mori, Koichi; Maruyama, Koh-ichi, Magnetic Science Joint Symposium 2004, 2004, 3AP22 for reference.).
This magnetostriction measured by the publicly known method, is not the average value on the whole volumes of the bulk in the sample, but a local value of the volumes near the surface where the X-ray beam irradiates and interacts while diffraction. By using this publicly known method, magnetostriction can be measured nonelectrically, noncorrecting, and noncontactually by X-rays. In the experiments, for the shift ΔθB and the magnetostriction λ100, the dependency on θ could not be detected. Thus, in the left hand side of equation [No. 6], it could simply be noted λ100(H).
Under extreme conditions such as low temperature, or high magnetic field, being under the effect of thermal contraction or thermal conduction and magnetoresistance effect peculiar to electric devices, the calibration of the devices to measure the magnetostriction may sometimes be difficult. Under such extreme condition, property measurement devices may not be able to work with its own sensitivity as it worked at room temperature (See above mentioned “Theory of High-Temperature Magnetostriction” for reference.).
For example, concerning the magnetostrictive coefficient of iron at low temperature close to 200K, there are various opinions as shown in FIG. 3 (See above mentioned Magnetostriction: theory and applications of magnetoelasticity and Magnetic Science Joint Symposium 2004, 2004, 3AP22 for reference.). Here, the vertical axis in FIG. 3 is 106×λγ,2 axis and the horizontal axis represents the sample temperature T (K). The reason for various reports to arise in the magnetostrictive coefficient of iron is the difficulty of its calibration and correction at low temperature and high magnetic field. More specifically, at the present state, even for industrially important materials such as iron, the scientific basic property which ought to be a universal value unique to a substance, is not determined precisely whether they are correctly measured or not.
For measuring the magnetostrictive coefficient, owing to definition, it is necessary to confirm these magnetization states of the sample material to be measured, that they are in the demagnetized state and saturation magnetization state. In other words, for the measurement of magnetostriction, the measurement of magnetization on the sample material is necessary.
Conventionally, it is commonly known to provide two devices for measuring magnetostriction and magnetization respectively. Therefore, one must use a device based on the principle of magnetostriction measurement, having a sensitive probe at the region of interest volume of the sample, together with a device based on the principle of magnetization measurement, having a sensitive probe at the region of interest volume of the sample and efforts were made to measure them at the same volumes of the sample. As long as two devices are used for the observation of magnetostriction and magnetization at the same volume, ultimately, there are cases in which it has to be assumed that the observations are performed at the coextensive volumes.
In many cases, this assumption that the magnetostriction and the magnetization are observed at the coextensive volumes is accepted. But the fact that the devices are different for the measurements of the magnetostriction and the magnetization, means that both devices must be prepared respectively. In addition, in cases where the principles or the sensitive volumes of the probes are different, or, where either of the measurements cannot be preferably done under a certain condition, the assumption that the observations are performed at the coextensive volumes cannot always be accepted. The conventional method is insufficient in this point.
Under extreme conditions such as low temperature, whereas such a property as the magnetostriction of iron, one of the typical magnetic substances, has not been well determined, a standard sample for calibration of devices with known features, cannot be found at the moment.
For the measurements of the magnetostriction and the magnetization, if the observations at the coextensive volumes are not accepted, since too much magnetic field strength must be applied in order to saturate the magnetization, it may be harmful on its correction.
Thus, it is clear that the development of a method which enables the measurement of the magnetostriction and the magnetization at the exact coextensive volumes, without assumption, and under any measurement conditions, is useful.